The present invention relates to a color filter suitable for a combined use with a liquid crystal or an image sensor. The color filter of the invention can be used for a display and image scanner in a television receiver, video monitor or computer, etc. In the prior art, a color liquid crystal display formed by a liquid crystal for controlling the transmission or reflection of light and a color filter, has the color filter prepared by forming red, green and blue picture elements and a black matrix on a glass substrate by means of a dyeing process, a printing process or the like. Particularly when an image of high precision is required, a color filter prepared by a dyeing process is mainly used. A color image scanner also has a color filter formed in the same manner as above. However, prior color filters have had the following problems.
A color filter prepared by the dyeing process is prepared by dyeing a natural photosensitive resin such as gelatine and the like or a photosensitive synthetic resin such as amine-modified polyvinyl alcohol and the like with a dye such as acid dye on dyeing substrate. However, this type of color filter is unsatisfactory in reliability in its light resistance, heat resistance, moisture resistance, etc. On the other hand, color filters prepared by printing process are produced by the use of an ink prepared by dispersing a pigment into a thermosetting resin or an ultraviolet-curable resin, and this type of color filter is unsatisfactory in its ability to give a pattern of high precision and in attaining a surface smoothness of surface. Although Japanese patent application Kokai (Laid-Open) No. 60-237,403 discloses a color filter prepared by dispersing a pigment into a photosensitive a polyimide resin, polyimide resin is disadvantageous in that an absorption appears in the visible region to deteriorate the color reproducibility when its thickness exceeds 1.0 micron. Particularly when the field strength and light path length of a cell gap must be varied by changing the thicknesses of red, green and blue picture elements (hereinafter referred to as "multi-gap") in order to improve the contrast, it is difficult to realize a color reproducibility comparable to that of CRT (cathode ray tube).
As to the photo-polymerization initiator for photosensitive resins, polycyclic quinone compounds such as anthraquinone, naphthoquinone and the like have hitherto been used. However, they are practically disadvantageous in that they are low in sensitivity and particularly when a pigment is present the picture element formation by light irradiation takes a long period of time.
If pigment concentration is enhanced in order to achieve a good color reproducibility, no satisfactory polymer can be obtained by light irradiation only, so that the product is poor in adhesive property, cannot form a clear image upon development, and is low in environmental reliability. Although a dispersion composition prepared by dispersing a pigment into a natural photosensitive resin or a photosensitive polyvinyl alcohol resin was also proposed, it was inferior in resolution and, sensitivity, as well as stability in dispersion of the pigment. Further, a color filter made from such a dispersion composition was inferior in heat resistance and moisture resistance.
If a pigment is dispersed as it is, it is difficult to disperse the pigment finely because of agglomeration, association, etc. of the pigment in the dispersion. If it is again dispersed, the pigment again agglomerates, so that the stability of the dispersion is not good enough.
If, in the electrode structure of color filter, a transparent electrode such as ITO (indium tin oxide) or the like is provided on a transparent substrate such as a glass substrate and a color filter is constructed thereon, the insulating layer lowers the voltage, so that a higher voltage must be applied to the panel in order to achieve the desired liquid crystal panel characteristics. Particularly in the case of a multi-gap panel, it becomes impossible to vary the voltage in accordance with picture elements of red, green and blue. Further, another problem occurs in that, when a TFT element (thin-film transistor element) composed of amorphous silicon is used, the light must be screened, and therefore the concentration of pigment such as carbon in the black matrix must be enhanced sometimes. In such a case, that part becomes different from other picture elements in its insulating property, which is disadvantageous.